Transmission line arc detection and location system

ABSTRACT

DETECTION OF AN ARC ALONG A TRANSMISSION LINE AND LOCATION OF THE POINT ALONG THE LINE AT WHICH THE ARC WAS IGNITED IS ACHIEVED BY DETECTING AND COUNTING PEAKS OF THE STANDING WAVE THAT MOVES WITH, AND PRECEDES, THE ARC AS THE ARC TRAVELS BACKWARD TOWARD THE SOURCE OF POWER CARRIED BY THE TRANSMISSION LINE.

United States Patent Inventors Joseph F. Lambden Randallstown; John E.Thompson, Glen Burnie, Md. App]. No. 872,894 Filed Oct. 31, 1 969Patented June 28, 1971 Assignee Westinghouse Electric CorporationPittsburgh, Pa.

TRANSMISSION LINE ARC DETECTION AND LOCATION SYSTEM 11 Claims, 3 DrawingFigs.

US. Cl. 317/31, 317/50, 324/52, 324/585, 340/253 Int. Cl 1102b 3/20,GOlr 31/08 Field of Search 324/52,

58.5 (B), (inquired); 317/31, 50; 340/253 r INDICATOR 2 COUNTER FILTER3O 2O DETE CTOR [56] References Cited UNITED STATES PATENTS I 2,717,9929/1955 Weintraub 2,931,975 4/1960 Bechtel 3,281,674 10/1966Landgraf.....

3,300,715 1/1967 Tresselt 3,364,421 1/1968 Bullwinkel 3,470,331 9/1969Barash et a1.

Primary ExaminerJames D. Trammeil Attorneys- F. 1-1. Henson and E. P.Klipfe] ABSTRACT: Detection of an are along a transmission line andlocation of the point along the line at which the arc,was ignited isachieved by detecting and counting peaks of the standing wave that moveswith, and precedes, the are as the arc travels backward toward thesource of power carried by the transmission line.

LOAD

TRANSMISSION LINE ARC DETECTION AND LOCATION SYSTEM BACKGROUND OF THEINVENTION 1. Field of the Invention The present invention relatesgenerally to the detection of faults, or causes of failure, ontransmission lines. In particular, the invention resides in methods andsystems for detecting the existence of arcing on high power transmissionlines and for locating the position at which the arc occurs.

2. Description of the Prior Art Transmission lines, whether of the openwire, multiwire cable, coaxial, or waveguide types, are subject tophysical breakdowns which increase the loading or apparent loading atpoints where such breakdowns occur. Accordingly, each breakdown reducesthe amount of energy which will ultimately be transferred from thegenerator, or source of energy for frequently results in an are whichcan travel along the line back toward the source of power and causeextensive damage to system components. Typically, it has heretofore beenthe practice to utilize a plurality of sensors along the line as a meansfor locating the point of ignition of the arc, but such a technique hasnot proven capable of accurately pinpointing the origin of the arebecause it only provides an indication that an arc has reached aparticular sensor. Since the sensors are usually widely separated, onecan merely deduce that the oint of ignition is somewhere between thefirst sensor indicating arrival of the arc and the sensor immediatelypreceding it toward the load. The are can be extinguished by simplyremoving power from the line, but this renders the line useless forfurther power transmission because as soon as power is reappliedrecognition of the arc will occur, unless the fault is located andrepaired.

It is apparent, then, that a method for detecting and accuratelylocating the origin of arcs along transmission lines is highlydesirable, and it is the principal object of the present invention toprovide such a method and to provide a system for practicing the method.

SUMMARY OF THE INVENTION Briefly, according to the present invention,peaks of the standing wave that results from reflection of energytransmitted along the line at the point of the arc, are detected as thestanding wave moves with the movement of the arc backward toward thesource of energy, preceding the arc front. Ignition of an arc isaccompanied by a sharp increase in reflected energy and this phenomenonalone may be detected to indicate the the wave moves along the line, ata preselected point where means are provided to couple energy from theline without normally appreciably disturbing the energy transmissionalong the line. Distance from this point to the origin of the arc isequal to the number of wavelengths of the standing wave passing thepoint from original detection of the arc to loss of detector output uponpassage of the standing wavebeyond that point. The loss of detectoroutput is utilized to initate turning off of the source of energy, toextinguish the arc and thereby prevent damage to system components.

BRIEF DESCRIPTION OF THE DRAWINGS In describing an exemplary embodimentof the invention in detail, reference will be made to the accompanyingdrawing, in which:

FIG. 1 is an overall schematic diagram of a transmission line and of anembodiment of the arc detection and location system used therewith;

FIG. 2 is a block diagram of an embodiment of a portion of the detectionand location system of FIG. 1; and

FIG. 3 is a wave diagram useful in explaining the operation of thesystem in locating the point at which the arc originated.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to theaccompanying drawing, the arc detector and locator of the presentinvention is utilized in conjunction with a transmission line 10 havinga source of power, designated by generator 12, connected to thetransmitting end of the line and a utilization system, designated byload 14, connected to the receiving end of the line. Transmission line10 must be capable of carrying high power from source 12 to load 14, butapart from that requirement and the capability to cooperate with thesource and the load as input and output devices, the specific type oftransmission line utilized is immaterial to the practice of theinvention. For the sake of example, however, let it be assumed thattransmission line 10 is a waveguide utilized between a transmitter and ahigh gain antenna.

As a consequence of a physical breakdown in line 10, characterized as afault, an arc may be ignited at a position of the fault, this pointbeing designated by reference numeral 15. The present invention relieson the fact that the position of such a fault appears to the incidentwave (transmitted from generator 12) to be a point of poor termination,or impedance mismatch, and that a considerable reflection of theincident power therefore occurs at that point. In actual practice, 25percent or more of the incident wave may be reflected at the point ofignition of the arc. The combination of the outgoing (incident) wave andthe reflected wave traveling in opposite directions on the line createsa standing wave along the line. Moreover, if the arc does not remainstationary but travels backward toward the power source 12, as istypically the situation encountered in practice, the apparent point ofpoor termination (i.e., of improper loading, differing considerably fromthe characteristic impedance of the line) moves with the arc.Accordingly, the voltage maxima of the standing wave follows themovement of the arc as it travels back toward the power source. Thereare two voltage maxima (peaks) each wavelength (of the transmittedenergy) ahead of the arc and these maxima maintain their distance aheadof the traveling arc. Thus, the voltage of the standing wave increasesand decreases twice each time the arc travels one wavelength of theenergy generated by source 12, at any point between the original faultand the source.

According to the present invention, apparatus for coupling energy fromtransmission line 10 is positioned at a point along the line preferablyrelatively close to source 12. This coupler 18 should absorb as littleof the transmitted energy as possible, so as not to interfereappreciably with power transmission under normal conditions. In thepresent embodiment a suitable coupler is a directional coupler arrangedto accept negligible power from the incident wave but to absorbconsiderable power from the reflected wave.

A peak detector 20 is connected to coupler 18 to sense the voltage peaksof the standing wave as that wave responds to the movement of the arctoward source 12. The output of the detector 20 is applied to a counter21 to count the peaks of the standing wave after filtering of thedetector output by a wave filter 23 for removing perturbations of amagnitude sufficient to produce erroneous counts, outside the range offrequencies of interest.

the arc is simply The distance, in wavelengths of the transmittedenergy, from the position of the coupler 18 to the point of ignition ofD=number of peaks/2 By applying the output of counter 21 to adivide-by-two circuit 25, and the resulting signal to an indicator 28scaled in terms of wavelength, the precise distance of the origin of theare from the coupler 18 (or from any other point along the line, byappropriate scaling of the indicator) is presented in any desired units.

To prevent damage to any components of the system at the source end ofthe line, or in the detecting apparatus. the loss of detector outputwhich occurs when the standing wave passes the coupler is sensed bylogic circuitry 30 which then operates to cut off the power source 12.When source 12 is deenergized the arc is extinguished. The logiccircuitry 30 may be implemented as shown in FIG. 2. A monostable, orone-shot, multivibrator 33 is connected to receive an input from theoutput of peak detector 20. Normally, with the detecting equipment inoperation, one-shot 33 is in its stable state and supplies apredetermined voltage level as an output thereof. This voltage level isselected to be adequate to actuate a cutoff switch 35, ordinarilysupplying energizing power to source 12, to the off condition in whichpower is removed from the source. A gate 36 is connected between theoutput circuit of one-shot 33 and the switch 35 and is normally in theblocking condition to prevent application of the cutoff voltage toswitch 35 when one-shot 33 is initially in its stable state. Gate 36 isalso connected to receive an input from the output of detector andresponds to a voltage level from the detector to switch to asignal-passing condition where it remains latched" until reset by asignal applied to a reset input lead thereto. in contrast, an outputvoltage emanating from detector 20 triggers one-shot 33 to itsquasi-stable state. If the delay time of the monostable multivibrator,i.e., the time interval between assumption of the quasi-stable state andreturn to the stable state, is set to be greater than one-halfwavelength of the energy transmitted from source 12, then one-shot 33cannot return to its stable state so long as detector 20 continues toproduce output pulses at a rate detennined by the passage of peaks ofthe standing wave at coupler 18.

In operation of the logic circuitry of FIG. 2, the first peak of thestanding wave detected by detector 20 results in an output voltage fromthe detector. Simultaneous application of this voltage to one-shot 33and to latching gate 36 causes the oneshot to assume the quasi-stablestate and to discontinue its output (or to reduce the output level to avalue far below that required to actuate switch 35),just as gate 36 isswitched from a blocking condition to a passing condition. While peaksof the standing wave continue to pass coupler 18, the one-shotmultivibrator is constrained to remain in quasi-stable state becauseeach output pulse of the detector restarts the delay time of themultivibrator and the interval between these output pulses is less thanthe delay time interval of the multivibrator. However, when the lastpeak of the standing wave preceding the traveling arc passes coupler l8,detector 20 ceases to produce an output, and at the conclusion of thedelay time interval following the last output pulse of the detector,multivibrator 33 reverts to its stable state in which its output voltageis suddenly returned to the aforementioned predetermined level. Gate 36,which remains latched in the passing" condition despite loss of detectoroutput, permits this voltage level to be applied to cutoff switch 35whereupon the power source 12 is deenergized and the arc isextinguished. The power source may be energized, after repair of thecause of the are using the fault location information obtained from thedetection system, but simply applying a reset signal to gate 36 toreturn the gate to the blocking" condition and thereby to remove thecutoff voltage from switch 35.

The basis of the distance measurement, while it should be quite clearfrom the preceding description, is further illustrated in FIG. 3. Thereflected wave that occurs upon ignition of the arc adds to the incidentwave at that point, to produce the standing wave 40. Voltage peaks ofthe standing wave occur along the line 10 at points x=n M14, where n isan odd integer, from the point of ignition. As the arc moves toward thesource of power at the transmitting end of line 10, the impedancemismatch which resulted in standing wave 40 moves with the frontalportion of the arc. Hence, the standing wave is not stationary, butsimilarly moves with the arc, and its two voltage peaks each wavelengthahead of the arc maintain their distance from the frontal portion of theare as the arc travels backward along the line. Detection of the numberof standing wave peaks passing a fixed point along the line is thustantamount to proportionally detecting the number of wavelengths fromthat point to the origin of the arc, i.e., to the location of the fault.

It should be apparent that the position of coupler 18 is preferablysufficiently close to source 12 to permit arc detection and location inproximity to the source of power, and yet not so close that insufficienttime is available between loss of detector output and arrival of the areat the power source to permit turning off the power source to extinguishthe arc and prevent damage to system components.

We claim:

l. A system for detecting an arc and for locating the point oforigination of the are along a transmission line carrying energy betweena source and a load, said system comprising:

means for sensing a substantial increase in reflected energy along saidline over the amount of reflected energy occurring under normalconditions, as a result of ignition of an arc on the line remote fromsaid source, said sensing means including;

means responsive to movement of said arc backward along said line towardsaid source, for detecting peaks of the standing wave produced by acombination of said reflected energy and of the outgoing energy fromsaid source, as said standing wave precedes said are in movementtherewith backward along said line.

2. The system according to claim 1 further including means responsive tocessation of detection of peaks by said peak detecting means for cuttingoff said source of energy to extinguish said arc.

3. The system according to claim 1 wherein said sensing means furtherincludes means positioned along said line at a point in proximity tosaid source of energy for coupling energy from said standing wave tosaid peak detecting means.

4. The system according to claim 1 wherein said sensing means ispositioned at a predetermined point in said line, and wherein is furtherincluded means responsive to the number of peaks of said standing wavedetected by said peak detecting means for indicating the distancebetween said predetermined point and the point of origination of saidare along said line.

5. The system according to claim 1 wherein said sensing means is locateda known distance from said source of energy, and wherein is furtherprovided means for counting the peaks detected by said peak detectingmeans for determining the distance between said source and the point ofignition of said arc on said line.

6. The system according to claim 5 further including means responsive tothe loss of output of said peak detecting means, as an indication of thepassage of said arc past the position of said sensing means in saidline, for deenergizing said source of energy to extinguish said arc.

7. The system according to claim 6 wherein said sensing means furtherincludes means positioned along said line at said known distance fromsaid source, for coupling energy from said standing wave to said peakdetecting means.

8. The method of detecting an are on a transmission line carrying highpower from a source to a load, and of locating the point of originationof said are on said line, including the steps of detecting peaks of thestanding wave produced by a combination of wave energy reflected fromthe arc and outgoing wave energy from said source, as said standing waveprecedes said arc in movement therewith backward along said line towardsaid source, at a predetermined point along said line in proximity tosaid source, and counting the detected peaks as a measure of thedistance of the point of origination of said are from said predeterminedpoint at which the peaks are detected. I

9. The method according to claim 8 further including the step of turningofi said source when peaks tease to be detected, to extinguish said arc.

10. The method according to claim 9 wherein said peak detecting stepincludes absorbing energy from said standing wave without appreciablydisturbing the normal flow of energy along said line toward said load.

11. A transmission line are detection and location system, comprising:

means positioned at a known point on said line for detecting peaks of amoving wave deriving from the addition of the wave incident on an are,if present on said line, and the wave reflected from said arc, saidmoving wave traveling ahead of said are as it moves toward a source ofsaid energy; and

means responsive to the detected peaks for establishing the location ofthe ignition point of said are relative to said known point.

